A Tale of Two Kagome Magnets: From Nèel to Valence-bond Solid State

Kittiwit Matan (Mahidol University, Thailand)

Spin dynamics of two structurally similar spin-1/2 distorted kagome lattice antiferromagnets Cs2Cu3SnF12 and Rb2Cu3SnF12 will be discussed. Magnetic excitations in Cs2Cu3SnF12, which has an ordered ground state owing to strong Dzyaloshinskii-Moriya interactions, can be qualitatively described by linear spin-wave theory. However, we found that the excitation energies are renormalized by a factor of approximately 0.6. This negative renormalization is attributed to quantum fluctuations, and is in contrast to the positive quantum renormalization observed in a quantum-spin chain. On the other hand, magnetic excitations in Rb2Cu3SnF12, whose ground state is a "pinwheel" valence-bond solid state, can be understood in terms of singlet-to-triplet excitations. Recent high-intensity pulsed neutron scattering reveals a weak dispersive and "ghost" mode, which is attributed to an enlarged unit cell below a structural transition. We also observed continuum scattering at high energy, which is reminiscent of the fractionalized excitations recently observed in herbertsmithite. In addition, field-dependence of the singlet-to-triplet excitations will be discussed.

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